This invention relates generally to wrapping and packaging machines and more particularly concerns a horizontal wrapping machine utilizing a microprocessor-based control system (MBS) and method wherein separate drives and operating temperatures in the wrapping machine are independently servo controlled.
In a horizontal wrapping machine, a continuous film of packaging material is supplied from a roll and drawn past a former which shapes the film into a continuous tube of packaging material. Products to be wrapped are supplied through the former into the tube of packaging material such that the products are spaced apart from one another in the tube. The seam of the tube is longitudinally sealed and the tube of packaging material is then cut and transversely sealed as each product, carried within the tube, passes through a sealing and cutting station. In this way, an individual sealed package is formed about each product.
Typically, the products to be packaged are supplied to the former on an infeed conveyor in the form of an endless chain having a number of product pushers extending from the chain. Each adjacent pair of pushers defines an infeed conveyor flight, and each product is advanced to the former in an individual conveyor flight. As each product is advanced into the film former, it is picked up by the bottom surface of the interior of the now-formed film tube and carried in the tube to the cutting and sealing station.
The film is formed in the former such that the lateral edges of the film, when the tube is formed, extend downwardly from the center of the film tube in a side-by-side relationship. A number of pairs of finwheels rotating about vertical axes in a finwheel assembly engage opposite sides of the downwardly extending pair of film edges to drive the film toward the cutting and sealing station. At least one pair of finwheels in the finwheel assembly may be heated, serving to heat seal the downwardly extending film edges together to seal the tube of heat sealable film. Other so-called cold-seal film do not need heat but instead use the pressure of one or more finwheel assemblies to create the seal.
As the now-enclosed tube of film carrying products which are spaced apart from one another advances past the sealing and cutting station, opposed cut/seal heads, one containing a knife member and the other an anvil, are rotated into engagement with the film tube between each successive pair of products. The cut/seal head may also include heated members so as to seal the film as it is cut to thereby form individual sealed packages, each containing a now-wrapped product.
In the past, a typical horizontal wrapping machine has been driven by a single motor through a single line shaft. In such a wrapping machine, separate gear boxes, belt and pulley, and chain and sprocket drives are coupled to the main shaft and the infeed conveyor, the finwheel assembly, and the cut/seal heads.
There are a number of disadvantages associated with such prior art horizontal wrapping machines which are overcome by the horizontal wrapper disclosed in the present application. For example, in such prior horizontal wrapping machines, in order to change the cut length, i.e., the distance between cuts on the tube of film, it is necessary to make a number of mechanical adjustments to change drive ratios and the like. In the present wrapping machine, a change in cut length may be effected in a short period of time without the necessity of mechanical adjustments by merely entering a number on a keyboard entry device connected to the controlling microprocessor.
Also, in prior horizontal wrappers, different sections of the machine cannot be operated independently of other sections without the use of mechanical clutches. Such independent operation is desirable during servicing of the machine in order to isolate problems in machine operation. In the present horizontal wrapper, different sections of the wrapping machine can be driven separately, again under computer control.
Another problem with prior horizontal wrapping machines is a difficulty in reorienting the phasing of the cut-heads relative to the desired cut locations between the products in the tube of packaging material. In the presently disclosed horizontal wrapping machine, the velocity profile of the cut-heads is automatically adjusted for correct phasing when the package length is changed.
In addition, in prior horizontal wrappers, it has generally not been possible to readily vary the product pusher position relative to the film position in order to correct product registration errors. In the past, it has been necessary to stop the wrapping machine and disengage a mechanical clutch between the main drive and the pusher drive while reorienting the pusher chain relative to the main drive. In the presently disclosed horizontal wrapper, the pusher location relative to the film position is sensed and it is possible to advance or retard the pusher by adjusting the infeed conveyor velocity on a real-time basis. A related problem has been an inability of prior machines to change the product-to-film registration during operation of the machine. It has been necessary to stop the machine and adjust the pusher position relative to the main drive. In the present system, however, the product registration can be changed using operator accessible inputs without stopping the operation of the machine.
In order to obtain the above-mentioned advantages of the presently disclosed horizontal wrapping machine, the present wrapper includes three separate closed loop servo-controlled motor drives for the infeed conveyor, for the finwheel assembly which drives the film, and for the cut-head drive, respectively. Each closed loop servo control circuit includes a motor which is driven by a summing-amplifier. The summing-amplifier receives as a feedback signal the actual motor velocity and receives as a control signal a desired motor velocity. Each servo control circuit is thereby operable to maintain its associated motor at the velocity established by the desired velocity control signal. Each of the servo control circuits forms a part of a microprocessor-based controller which coordinates the motor speeds to effect the desired synchronous operation of the horizontal wrapping machine.
To produce an acceptable packaged product, it is necessary, within selected tolerances, for the package to contain a certain desired length of film and for the product to be at a desired location relative to the length of film, which is formed into a completed package. There is an additional positioning requirement which arises typically due to the provision of printed material on the packaging film. This requirement is that each length of film used to form a package should have thereon the properly-oriented printed matter for the package.
Thus, for example, if the product to be packaged is a candy bar having a length of two and one half inches, it may be desired to package the candy bar in a package having a length of packaging film of four inches. It may further be desired to center the candy bar in the package. The length of film used for the package, four inches, is the cut length of the package. The length of the candy bar, two and one half inches, is designated the product length. Thus, for each four inch cut length of packaging film, it is desired to have a candy bar centrally located therein. This meets the above-mentioned first two requirements of proper centering of the product in the package and of proper package length.
Typically, a candy bar wrapper contains printed matter including the name of the candy bar and its manufacturer, and perhaps a list of ingredients, etc. The name is typically in large letters extending across most of the length of the product. In order for the product name to be properly located on each package, not only must the package length be approximately equal to the desired cut length, but also the positioning of the product and cut relative to the printed matter must be approximately correct so that the product name lies on the product and not across a cut location on the film.
In the usual case, marks called "eyespots" are placed on the film, such as along one of the film edges, to provide a reference for the beginning and end of each cut length. It is therefore desirable that as each such indicated cut length of film moves past the film former that one product be placed in the film tube at the desired location relative to the beginning and the end of the cut length. Where each cut length is defined as beginning at a fixed relationship to an eyespot, the distance along the film tube from the eyespot to the trailing edge of the product is termed the product orientation. Thus, in the above-mentioned example, if the two and one half inch candy bar is to be centered in each package, and each cut is to be on an eyespot, then the desired product orientation is three and one-quarter inches.
Not only must the proper product orientation relative to the marked film be obtained, but the sealing and cutting by the cut/seal heads must also occur between the products. The heads will engage the film at an entered relationship to the film eyespots.
In the horizontal wrapping machine illustrated herein, the master control for each of the servo motors is derived from a master tachometer on the film drive mechanism. In the illustrated machine, a microprocessor-based controller receives the output from the master tachometer which relates to film speed. Based upon this actual film speed, the controller outputs the desired product infeed conveyor speed to the infeed conveyor motor summing-amplifier and outputs the desired cut/seal speed to the cut/seal head motor summing-amplifier.
To infeed one product per cut length of film, the desired infeed conveyor speed must be set to be a proportion of the actual film speed so that exactly one product is delivered to the film former for each cut length of film which passes the film former. To maintain proper product orientation relative to the film cut lengths, the controller varies the desired velocity signal supplied to the infeed conveyor servo loop to correct for errors in product orientation relative to the film.
The cut/seal heads may be viewed as operating in two modes. During a cut and seal mode, wherein the cut/seal heads are in contact with the film, their film-engaging faces must move at the same rate as the film. During what is termed a return mode, the cut/seal heads are not contacting the film. They must move at a different rate of speed, usually a higher rate, in order to be repositioned for the next cut and seal phase.
The microprocess-based controller supplies a desired cut/seal-head velocity to the cut/seal head servo motor amplifier during a cut cycle to move the film-engaging surfaces at a rate substantially equal to the film speed in the direction of film travel. During a return cycle, the controller supplies a desired velocity signal to the cut/seal head summing-amplifier, which is derived from the film velocity, such that the cut-heads are in proper position for the next cut cycle.